1. Field of the Invention
The present invention relates to an ionic electro-conductive resin and an electro-conductive member for electrophotography.
2. Description of the Related Art
In an electrophotographic apparatus, an ionic electro-conductive agent such as a quaternary ammonium salt is added to the electro-conductive layer of a charging roller, which is placed to abut on an electrophotographic photosensitive member and charges the electrophotographic photosensitive member, for adjusting the electro-conductivity of the electro-conductive layer.
However, the environmental stability of the electrical resistance value of the electro-conductive layer whose electro-conductivity has been adjusted with the ionic electro-conductive agent largely depends on the water capacity of the electro-conductive layer. Here, the water capacity of the electro-conductive layer refers to the amount of water molecules in the electro-conductive layer. Particularly under a low-temperature, low-humidity environment, specifically, for example, under an environment having a temperature of 15° C. and a humidity of 10% RH, the water capacity of the electro-conductive layer reduces and hence the electrical resistance of the charging roller increases. When such charging roller is used in the formation of an electrophotographic image and a high-definition electrophotographic image is output at high speed, a defect such as a streak is liable to occur in the electrophotographic image to be obtained.
To cope with such problem, Japanese Patent Application Laid-Open No. 2009-237359 discloses an approach to stabilizing an ion carrier in a polymer with an epoxy compound having an alkylene oxide structure and a curing agent.
In addition, Japanese Patent Application Laid-Open No. H07-121009 discloses an approach involving introducing a hydroxyl group into a polymer with a vinyl monomer having the hydroxyl group to increase a hydration amount. It should be noted that the hydration amount refers to the amount of water molecules held on the periphery of an ion exchange group.
In the approach of Japanese Patent Application Laid-Open No. 2009-237359, the alkylene oxide structure forms a coordination bond with the ion carrier or an ion exchange group by virtue of a lone pair of electrons which an oxygen atom has, thereby exerting a suppressing effect on the recombination of the ion exchange group and the ion carrier. In addition, the lone pair of electrons and a water molecule electrically attract each other, and hence the water capacity in the electro-conductive layer can be maintained. However, the coordination bond has a small binding energy. Accordingly, with the alkylene oxide structure alone, a water molecule evaporates from the electro-conductive layer in a low-temperature, low-humidity environment. Therefore, when an application to the charging roller is taken into consideration, it is difficult to obtain sufficient electro-conductivity in the low-temperature, low-humidity environment merely by introducing the alkylene oxide structure into the structure of the electro-conductive layer. By the foregoing reason, in the structure of Japanese Patent Application Laid-Open No. 2009-237359, an ionic electro-conductive agent is added for obtaining an electrical resistance value in a moderate resistance region needed for the charging roller even in the low-temperature, low-humidity environment. However, the addition of the ionic electro-conductive agent leads to the movement of the ionic electro-conductive agent in the electro-conductive layer, thereby causing the contamination of the photosensitive member due to bleeding or blooming.
In addition, in the approach of Japanese Patent Application Laid-Open No. H07-121009, the hydroxyl group is introduced into the polymer to increase the hydration amount on the periphery of the ion exchange group. Thus, the water capacity in the electro-conductive layer in a low-temperature, low-humidity environment can be increased. According to investigations conducted by the inventors of the present invention and the like, however, upon high-speed output of a high-definition image in the low-temperature, low-humidity environment, a variation in electrical resistance value of the entire charging roller occurs owing to the insufficiency of the hydration amount on the periphery of the hydroxyl group. As a result, an image failure such as a charging horizontal streak or a sandy image is caused in some cases. Thus, the inventors have acknowledged that the approach still has room for improvement.